1. Field of the Invention
The present invention relates to solid catalyst materials that have been preactivated using co-catalyst components that may be subjected to prepolymerization, and the use thereof in the production of polyolefins. The invention also relates to preparing the preactivated and/or prepolymerized catalysts separate from the principle polymerization system, separating the catalysts from their reaction mixture and then using the catalysts in a method of making a polyolefin. The preactivated and/or prepolymerized catalysts preferably are carried into the polymerization reactor in a carrier containing at least an inert gas and a liquid solvent.
2. Description of Related Art
Ziegler-Natta catalysts are well known for catalyzing the polymerization of olefins. Conventional Ziegler-Natta catalysts are those that contain a procatalyst made from contacting an internal electron donor, a titanium source, a magnesium source and a halogenating agent (which may be combined with one of the other components). This procatalyst then typically is combined with an external selectivity control agent (xe2x80x9cSCAxe2x80x9d) and an aluminum alkyl to produce the Ziegler-Natta catalyst system. See, e.g., U.S. Pat. No. 4,393,182 to Job. Generally, the selectivity control agents may be any of several classes of electron donative compounds, but one class that has been studied extensively is the class of organosilicon compounds having at least one Sixe2x80x94O (i.e., siloxy) bond. These compounds include tetra, tri, bi and mono alkoxy silanes. While these SCAs are good selectivity control agents, they usually provide for only a limited range of polymer product properties, such as a narrow range of available polymer molecular weight distribution (MWD) within the range that is available through the use of various internal electron donors.
It is known that any two of the three final components of the catalyst system may be brought together shortly before introduction into the primary polymerization reactor. Also, it is known that all three components may be brought together (the procatalyst, co-catalyst, and SCA) prior to introduction to the polymerization reactor in a method known as preactivation. Finally, it is also known that the preactivated material, either separately or simultaneously, may be exposed to an olefin (procatalyst, co-catalyst, SCA(s) and monomer(s)) to form a prepolymer, and then subjecting the prepolymer to primary polymerization in a primary polymerization reactor. The preactivation and prepolymerization methods especially serve to form highly active catalysts.
When such highly active catalysts are used, the polymerization in the polymerization reactor begins very rapidly, immediately upon introduction of the preactivated catalyst and/or prepolymerized catalyst to the reactor. The rapid reaction results in an attendant rapid rise in reaction temperature causing overheating, undesirable formation of agglomerates, coagulation of polymer, and ultimately, reactor failure. This is particularly true in gas phase polymerization systems. To avoid this rapid rise in temperature, preactivated and prepolymerized catalysts may be fed directly to the polymerization reactor in the slurry or suspension in which the catalysts were formed (i.e., on-line or in-line). It previously was thought that feeding a preactivated and/or prepolymerized catalyst to a gas phase reactor in solid form (together with additional co-catalyst, SCA(s), monomer(s), recycle and condensed gas, etc., as needed; i.e., off-line prepared catalyst material) would cause immediate and intense reaction inside the gas phase reactor resulting in the aforementioned disadvantages.
U.S. Pat. No. 4,721,763 discloses a process for polymerizing olefins whereby a prepolymerization stage is conducted in a liquid phase prior to gas phase polymerization. In this process, prepolymerization is effected by contacting the olefin with a Ziegler catalyst system in the liquid phase (suspension or slurry) and then subjecting the prepolymerized catalyst to a second prepolymerization in the gas phase and then subjecting that prepolymer to polymerization in the gas phase. Thus, the activity of the catalyst is reduced significantly before being fed to the full-scale polymerization reactor by conducting two prepolymerization steps. The two-stage prepolymerization approach is very costly and an inefficient mechanism to prepolymerize a catalyst.
U.S. Pat. No. 5,610,244 discloses a process for polymerizing ethylene in a fluidized bed whereby a titanium or vanadium-containing catalyst component is preactivated or prepolymerized prior to being fed to a gas phase polymerizer. The precontacting and prepolymerization are conducted in-line whereby the solid catalyst component and co-catalyst (triethylaluminumxe2x80x94TEAL) are contacted briefly, and then they are fed to a prepolymerizer loop reactor and then fed directly to the reactor.
International Patent Publication No. WO 88/02376 discloses a process for polymerizing olefins whereby a solid magnesium and titanium-containing catalyst procatalyst component is prepolymerized prior to being fed to a gas phase reactor. In accordance with the process, the catalyst components are contacted with monomer in a liquid phase loop reactor to form a prepolymer, whereby the weight ratio of monomer to solid catalyst procatalyst component is at least about 6000:1, and the residence time is less than 400 seconds. The prepolymer then is directly fed in-line together with the other unreacted components to a gas phase reactor. On-site in-line preactivation and prepolymerization may help to solve the problem of excess heat generation by feeding the components in a liquid stream to the reactor, but it requires additional processing and additional equipment at the gas phase polymerization plant. In addition, these in-line preactivation and prepolymerization methods typically do not result in any significant savings in terms of raw material usage, or in capital cost savings at the polymerization plant.
There exists a need to develop preactivated or prepolymerized catalysts that can be prepared off-line and sold to polymer manufacturers. There also exists a need to provide polymer manufacturers with extremely high activity catalysts, such as preactivated and/or prepolymerized catalysts, that do not result in rapid rise in reaction temperature causing overheating, undesirable formation of agglomerates, coagulation of polymer, and ultimately, reactor failure. In addition, there exists a need to provide a preactivated and/or prepolymerized catalyst that can be used to polymerize olefins in high yield using less solid catalyst and external selectivity control agent (SCA).
It is therefore a feature of the invention to provide preactivated and/or prepolymerized catalysts that can be used to make polyolefin polymers in high yield at high production rates and at reduced costs. It is an additional object of the present invention to provide an economically efficient method of making polyolefin polymers using preactivated and prepolymerized catalysts resulting in polymers with improved physical properties, including, for example, increased bulk density, decreased average particle size and varied molecular weight distribution (MWD).
In accordance with these and other features of the present invention, there is provided a solid preactivated catalyst component that includes (a) a solid procatalyst component which is the reaction product of a magnesium compound, a tetravalent titanium halide and an internal electron donor, with (b) a cocatalyst, and (c) at least one silicon compound. The solid preactivated catalyst component is prepared by a process comprising contacting a procatalyst (A) comprising the reaction product of (i) a magnesium compound, (ii) a tetravalent titanium halide and (iii) an internal electron donor, with (B) a co-catalyst, and (C) at least one silicon-containing external electron donor, which may be the same or different than the internal electron donor (iii) to form a solid preactivated catalyst. The solid preactivated catalyst then is separated from the remaining components of the mixture resulting from contacting the aforementioned components, and then dried to form a dry, solid preactivated catalyst component. The catalyst components preferably are contacted for a period of time sufficient to form a preactivated catalyst which can be fed immediately or later to a polymerization reactor, or which can be prepolymerized prior to feeding to a polymerization reactor.
In accordance with another feature of the invention, there is provided a method of polymerizing an olefin in the gas phase comprising polymerizing an olefin monomer in a gas phase reactor in the presence of the aforementioned solid preactivated catalyst, a co-catalyst and an external electron donor, wherein the amount of the external electron donor used is from 10 to 90% of the amount of external donor that would be used with the same catalyst components that were not preactivated. In the method, the preactivated catalyst preferably is fed to the reactor in an inert carrier.
In accordance with another feature of the invention, there is provided a prepolymerized olefin polymerization catalyst prepared by a process comprising contacting a procatalyst (A) comprising the reaction product of (i) a magnesium compound, (ii) a tetravalent titanium halide and (iii) an internal electron donor, with (B) a co-catalyst, and (C) at least one silicon-containing external electron donor, which may be the same or different than the internal electron donor (iii) to form a solid preactivated catalyst. The solid preactivated catalyst then is contacted with an olefin monomer to form a solid prepolymerized catalyst. The solid prepolymerized catalyst then is separated from the remaining components of the mixture resulting from contacting the preactivated catalyst with the monomer. Finally, the solid prepolymerized catalyst is dried to form a dry, solid prepolymerized catalyst.
In accordance with yet another feature of the invention, there is provided a method of polymerizing an olefin in the gas phase comprising polymerizing an olefin monomer in a reactor in the presence of the aforementioned prepolymerized catalyst, a co-catalyst and an external electron donor, wherein the amount of the external electron donor used is from 10 to 90% of the amount of external donor that would be used with the same catalyst components that were not prepolymerized. In the method, the prepolymerized catalyst preferably is fed to the reactor in an inert carrier.
In accordance with another feature of the invention, there is provided a method of making a preactivated catalyst comprising contacting a procatalyst (A) comprising the reaction product of (i) a magnesium compound, (ii) a tetravalent titanium halide and (iii) an internal electron donor, with (B) a co-catalyst, and (C) at least one silicon-containing external electron donor, which may be the same or different than the internal electron donor (iii) to form a solid preactivated catalyst. The solid preactivated catalyst then is separated from the remaining components of the mixture resulting from the above-mentioned contacting. The separated preactivated catalyst then is dried to form a dry, solid preactivated catalyst.
These and other objects of the invention will be readily apparent to those skilled in the art upon reading the detailed description of preferred embodiments that follows.